Switch element comprising a liquid-crystalline medium

ABSTRACT

The present invention relates to a switch element, which is thermoresponsive and which switches between a less transmissive state for radiant energy and a more transmissive state for radiant energy, and which comprises a liquid-crystalline medium. The invention furthermore relates to the use of the switch element for the regulation of radiant energy flow between interior spaces and the environment and for the regulation of the temperature of interior spaces. The invention furthermore relates to a liquid-crystalline medium, characterized in that it comprises a compound of the formula (I), in particular for use in the switch elements according to the invention.

The present invention relates to a switch element, which isthermoresponsive and which switches between a less transmissive statefor radiant energy and a more transmissive state for radiant energy, andwhich comprises a liquid-crystalline medium. The invention furthermorerelates to the use of the switch element for the regulation of radiantenergy flow between interior spaces and the environment and for theregulation of the temperature of interior spaces. The inventionfurthermore relates to a liquid-crystalline medium, characterised inthat it comprises a compound of the formula (I), in particular for usein the switch element mentioned above.

The switch element is used in accordance with the invention in windowsor comparable openings in buildings, such as, for example, in glazeddoors, skylights and/or glass roofs for the regulation of light influx.

For the purposes of this invention, the term liquid-crystalline mediumis to be taken to mean a material or compound which under certainconditions shows liquid-crystalline properties. Preferably, theliquid-crystalline medium shows thermotropic behavior, more preferably,the liquid-crystalline medium exhibits a temperature-induced phasetransition from an isotropic to a liquid-crystalline phase, mostpreferably to a nematic phase.

For the purposes of this invention, the term interior space is intendedto be taken to mean both interior spaces in private, public orcommercial buildings, for example buildings used for office purposes,and also the interior spaces of vehicles. Furthermore, the term interiorspace is also intended to be taken to mean the interior spaces ofbuildings used purely commercially, such as, for example, greenhouses.

For the purposes of this invention, the term window is intended to betaken to mean any desired light-transmissive openings sealed by solidmaterial in buildings, in transport containers or in vehicles.

For the purposes of this invention, radiant energy flow is taken to meanthe flow of electromagnetic radiation which emanates from the sun, hitsthe earth after passing through the atmosphere and is only absorbed to asmall extent, or not at all, by glass sheets. The electromagneticradiation may alternatively also emanate from light sources other thanthe sun. Since relatively short-wavelength radiation (UV-B light) andlong-wave-length infrared radiation are absorbed by the atmosphere or byglass sheets, for the purposes of this invention, the term “radiantenergy” is understood to comprise UV-A light, light in the visibleregion (VIS light) and near-infrared (NIR) light.

The term light, unless defined more precisely, is likewise intended tobe taken to mean electromagnetic radiation in the UV-A region, VISregion and near-infrared region.

According to commonly used definitions in the field of physical optics,for the purposes of this invention, UV-A-light is understood to beelectromagnetic radiation of 320 to 380 nm wavelength. VIS-light isunderstood to be electromagnetic radiation of 380 to 780 nm wavelength.Near-infrared light (NIR) is understood to be electromagnetic radiationof 780 to 3000 nm wavelength.

Therefore, for the purposes of this invention, the terms “radiantenergy” and “light” are understood to be electromagnetic radiation of320 to 3000 nm wavelength.

For the purposes of this invention, the term switch element thus denotesa device capable of switching between a state in which it has lowertransmission for radiant energy and a state in which it has highertransmission for radiant energy, the term radiant energy being definedas above. The switch element may selectively switch in one or moresub-regions of the spectrum of radiant energy. The terms “device” and“switch element” are being used interchangeably in the following.

The switch element according to the invention is thermoresponsive.However, it may additionally also be controlled by one or more othermechanisms, for example by electrical current or mechanical mechanisms.Preferably, such other mechanisms are not present.

Modern buildings are distinguished by a high proportion of glasssurfaces, which is desired both for aesthetic reasons and also inrelation to the brightness and comfort of the interior spaces. It hasbecome equally important in recent years that buildings used for livingor commercial purposes and/or which are accessible to the public havehigh energy efficiency. This means that as little energy as possible hasto be expended for heating purposes in the cold season in temperateclimatic zones (where the majority of highly developed industrialnations are located) and no or only little air conditioning of theinterior spaces is necessary in the warm season.

However, a high proportion of glass surfaces hinders the achievement ofthese aims. In warm climatic zones and in the warm season in temperateclimatic zones, glass surfaces result in undesired heating of theinterior spaces when they are hit by solar radiation. This is due to thefact that glass is transparent to radiation in the VIS and NIR region ofthe electromagnetic spectrum. Objects in the interior space absorb theradiation that is allowed through and are warmed thereby, which resultsin an increase in the temperature of the interior space (greenhouseeffect).

This increase in temperature of the interior space behind a glasssurface which is called greenhouse effect is due to the fact that theobjects in the interior which have absorbed the radiation will also emitradiation. However, the emitted radiation of these objects is mainly inthe infrared spectrum (typically about 10,000 nm wavelength) of light.It therefore cannot pass through the glass again and is “trapped” in thespace behind the glazing.

However, the above-described effect of glass surfaces in buildings isnot generally undesired: at low outside temperatures, in particular incold climatic zones or in the cold season in temperate climatic zones,heating of the interior spaces owing to solar radiation due to thegreenhouse effect may be advantageous since the energy requirement forheating is thereby reduced and costs can thus be saved.

With the increasing importance of energy efficiency of buildings, thereis therefore a growing demand for devices which control the flow ofenergy through windows or glass surfaces. In particular, there is ademand for devices which enable the flow of energy through glasssurfaces to be matched to the conditions (heat, cold, high solarradiation, low solar radiation) prevailing at the particular time.

Of particular interest is the provision of such devices in temperateclimatic zones, in which a seasonal change occurs between warm outsidetemperatures combined with high solar radiation and cold outsidetemperatures combined with low solar radiation.

The prior art discloses both non-switchable devices, which limit theenergy flow, but cannot be adapted in a variable manner, and alsoswitchable devices, which are able to match the energy flow to therespective conditions prevailing. Amongst the switchable devices, adistinction should be made between devices which do not adaptautomatically to the ambient conditions and devices which adaptautomatically to the ambient conditions. The latter devices are alsoknown as smart windows.

In order to improve the thermal insulation of windows, multiple-glazedwindow units (insulated glass units, IGU) have been known for some time.The sequence of two or more glass panes which enclose one or moregas-filled interspaces which are insulated from the environment enablesthermal conduction through windows to be significantly reduced comparedwith single-glass panes. The prior art furthermore discloses the coatingof glass surfaces with thin layers, e.g. metal or metal oxide layers(U.S. Pat. No. 3,990,784 and U.S. Pat. No. 6,218,018).

If the radiant energy flow is controlled exclusively by a coatingtechnique of this type and/or by the use of insulating glass, however,adaptation to varying weather or seasonal conditions is not possible.For example, it would be of interest for windows to be totallytransparent to sunlight at cold outside temperatures in order to reducethe energy consumption for heating. Conversely, it would be desirablefor windows to allow less sunlight to pass through at warm outsidetemperatures, so that less heating of the interior spaces takes place.

There is therefore a demand for devices in which the radiant energy flowcan be matched to the respective conditions prevailing. In particular,there is a demand for devices which are able to adapt automatically tothe ambient conditions.

The prior art discloses devices which, on application of an electricalvoltage, can be switched reversibly from a light-transmissive state to aless light-transmissive state. The first state will be referred to asbright state in the following, whereas the second state will be referredto as dark state.

A possible embodiment of electrically switchable devices areelectro-chromic devices, which are presented, inter alia, in Seeboth etal., Solar Energy Materials & Solar Cells, 2000, 263-277. A furtherreview is offered by C. M. Lampert et al., Solar Energy Materials &Solar Cells, 2003, 489-499.

Further electrically switchable devices known from the prior art arebased on the alignment of molecules of a liquid-crystalline medium onapplication of an electric field. Such devices are disclosed, interalia, in U.S. Pat. No. 4,268,126, U.S. Pat. No. 4,641,922, U.S. Pat. No.5,940,150 and WO 2008/027031 and likewise switch under electricalcontrol from a bright state to a dark transparent state.

Although the electrically switchable devices mentioned above enable theradiant energy flow to be set, they have the disadvantage of having tobe electrically controlled.

It would be desirable to have available a switch element which adaptsautomatically to the ambient conditions and which does not have to becontrolled either manually or by any additional coupled device capableof giving a signal upon a detected temperature deviation.

It would furthermore be desirable to have available a switch elementwhich does not require any electrical circuits. The introduction ofelectrical circuits into windows is accompanied by additional workduring manufacture of the windows and entails the risk of susceptibilityto flaws or a short service life of the devices. Furthermore, additionalinfrastructure is necessary for such devices, including electrical powersupply.

Devices which are not electrically switched, but instead are, forexample, temperature-controlled (thermoresponsive devices), aredescribed, inter alia, in Nitz et al., Solar Energy 79, 2005, 573-582. Apossible embodiment of such devices are systems which are based on theseparation between two phases above a certain temperature. Furtherembodiments are based on temperature-dependent properties of hydrogels.However, these devices typically switch between a transparent state anda dark translucent state, which is undesired for applications in whichit is required that the device stays transparent also in the dark state.

US 2009/0015902 and US 2009/0167971 disclose optical switch elementscomprising a liquid-crystalline medium between two polarisers. Theliquid-crystalline medium has the property of rotating the plane ofpolarisation of the light at a first temperature and not rotating oressentially not rotating the plane of polarisation of the light at asecond temperature. Thus, a suitable arrangement of the polarisersenables the devices to allow more light to pass through at the firsttemperature than at the second temperature. The twotemperature-dependent states represent a bright state (firsttemperature) and a dark transparent state (second temperature), and arepreferably caused by a change of the liquid-crystalline medium from anematic state (first temperature, liquid-crystalline medium is rotatingthe plane of polarisation of light) to an isotropic state (secondtemperature, liquid-crystalline medium is not rotating the plane ofpolarisation of light).

The applications US 2009/0015902 and US 2009/0167971 furthermoredisclose that liquid-crystalline media having a low clearing point aresuitable for use in the said devices. The switching process from thebright state to the dark transparent state, which is caused by the phasetransition of the liquid-crystalline medium, is intended to take placemerely on heating of the device by the typical radiation intensity ofthe sun in the warm season. To this end, a preferred clearing point ofbelow 85° C. is disclosed. An example disclosed is a liquid-crystallinemedium which comprises the liquid-crystalline mixture E7 together withadded 4′-hexyl-4-cyanobiphenyl (6CB) and which has a clearing point of35° C. It is furthermore generally disclosed in the above-mentionedapplications that the liquid-crystalline mixture ZL11132 (Merck KGaA)with a clearing point of 72° C. can alternatively also be used as thebasis for the preparation of liquid-crystalline media for use in theswitchable devices. However, no specific illustrative embodiments aredisclosed in this respect.

In this respect, it is to be noted that the modification of mixture E7disclosed in US 2009/0015902 and US 2009/0167971 by addition ofalkylcyanobiphenyl compounds, such as, for example,4′-hexyl-4-cyanobiphenyl, has the disadvantage that the low-temperaturestability of the liquid-crystalline medium is impaired.

A good low-temperature stability of the liquid-crystalline medium ishowever highly desirable, since in many applications, the switch elementis exposed to low temperatures for extended periods of time.

There continues to be a demand for liquid-crystalline media which aresuitable for use in thermally switchable devices. In particular, thereis a demand for liquid-crystalline media which show a transition from anematic state to an isotropic state (clearing point) at a temperaturewhich is within the operating-temperature range of the switch element.There is furthermore a demand for liquid-crystalline media which have ahigh content of cycloaliphatic and/or aromatic three-ring compounds,since such three-ring compounds can be prepared cost-effectively. Thereis furthermore a demand for liquid-crystalline media which have goodlow-temperature storage stability, preferably in combination with theproperties mentioned above.

To this end, the present invention provides a switch element,characterised in that it is thermoresponsive and that it switchesbetween a less transmissive state for radiant energy and a moretransmissive state for radiant energy, comprising a liquid-crystallinemedium, which comprises one or more compounds selected from compounds ofthe formula (I)

where

-   R¹¹ is H, F, Cl, CN, NCS, R¹—O—CO—, R¹—CO—O—, an alkyl, alkoxy or    thioalkoxy group having 1 to 10 C atoms, or an alkenyl, alkenyloxy    or thioalkenyloxy group having 2 to 10 C atoms, where one or more H    atoms in the groups mentioned above may be replaced by F, Cl, CN,    and where one or more CH₂ groups in the groups mentioned above may    be replaced by O, S, —O—CO— or —CO—O—;-   R¹² is selected from F, Cl, alkyl and alkoxy groups having 1 to 10 C    atoms, and alkenyl and alkenyloxy groups having 2 to 10 C atoms,    with the proviso that in the above-mentioned groups one or more H    atoms are replaced by F or Cl;-   R¹ is, identically or differently on each occurrence, an alkyl or an    alkenyl group having 1 to 10 C atoms, in which one or more H atoms    may be replaced by F or Cl;

are selected from

is selected from

and

-   X is on each occurrence, identically or differently, F, Cl, Br, CN    or an alkyl, alkoxy or thioalkoxy group having 1 to 10 C atoms,    where one or more H atoms in the groups mentioned above may be    replaced by F or Cl and where one or more CH₂ groups may be replaced    by O or S; and-   Y is on each occurrence, identically or differently, selected from H    and X; and-   Z¹¹ and Z¹² are, identically or differently, selected from CO—O—,    —O—CO—, —CF₂O—, —OCF₂—, —OCH₂—, —CH₂O—, —CH₂CH₂— and a single bond.

Preferentially, the liquid-crystalline medium furthermore comprises oneor more compounds of the formula (II)

where

-   R²¹, R²² are on each occurrence, identically or differently,    selected from H, F, Cl, CN, NCS, R¹—O—CO—, R¹—CO—O—, an alkyl,    alkoxy or thioalkoxy group having 1 to 10 C atoms and an alkenyl,    alkenyloxy or thioalkenyloxy group having 2 to 10 C atoms, where one    or more H atoms in the groups mentioned above may be replaced by F    or Cl, and where one or more CH₂ groups in the groups mentioned    above may be replaced by O, S, —O—CO— or —CO—O—;-   R¹ is defined as above;

are selected from

and

-   Y is on each occurrence, identically or differently, selected from H    and X;-   X is defined as above; and-   Z²¹ is selected from —CO—O—, —O—CO—, —CF₂O—, —OCF₂—, —CH₂CH₂—,    —OCH₂—, —CH₂O— and a single bond.

Preferentially, the liquid-crystalline medium furthermore comprises oneor more compounds selected from compounds of the formula (III)

where

-   R³¹ is H, CN, NCS, R¹—O—CO—, R¹—CO—O—, an alkyl, alkoxy or    thioalkoxy group having 1 to 10 C atoms, or an alkenyl, alkenyloxy    or thioalkenyloxy group having 2 to 10 C atoms, where one or more    CH₂ groups in the groups mentioned above may be replaced by O, S,    —O—CO— or —CO—O—;-   R³² is H, an alkyl or alkoxy group having 1 to 10 C atoms, or an    alkenyl or alkenyloxy group having 2 to 10 C atoms; and

are on each occurrence, identically or differently, selected from

andwhere Y and X are defined as above; and

-   Z³¹ and Z³² are, identically or differently, selected from CO—O—,    —O—CO—, —CF₂O—, —OCF₂—, —OCH₂—, —CH₂O—, —CH₂CH₂— and a single bond.

Preferentially, the liquid-crystalline medium furthermore comprises oneor more compounds selected from compounds of the formulas (IV), (V) and(VI)

where

-   R⁴¹, R⁴², R⁵¹, R⁵², R⁶¹, R⁶², are on each occurrence, identically or    differently, selected from H, F, Cl, CN, NCS, R¹—O—CO—, R¹—CO—O—, an    alkyl, alkoxy or thioalkoxy group having 1 to 10 C atoms and an    alkenyl, alkenyloxy or thioalkenyloxy group having 2 to 10 C atoms,    where one or more H atoms in the groups mentioned above may be    replaced by F or Cl, and where one or more CH₂ groups in the groups    mentioned above may be replaced by O, S, —O—CO— or —CO—O—;-   R¹ is defined as above;

are, identically or differently, selected from

is selected from

and a single bond;

-   Y is on each occurrence, identically or differently, selected from H    and X;-   X is defined as above; and-   Z⁴¹ to Z⁴³ and Z⁵¹ to Z⁵⁵ are, identically or differently, selected    from —CO—O—, —O—CO—, —CF₂O—, —OCF₂—, —CH₂CH₂—, —OCH₂—, —CH₂O— and a    single bond.

It should be noted that or the case that

represents a single bond, R⁶¹ and R⁶² are connected by a single bond, sothat a compound of the following formula results:R⁶¹—R⁶².

According to a preferred embodiment of the invention, theliquid-crystalline medium comprises one or more compounds of formula (I)and one or more compounds selected from compounds of the formulas (II),(III), (IV), (V) and (VI), as defined above. According to a particularlypreferred embodiment, the liquid-crystalline medium comprises one ormore compounds of formula (I) and one or more compounds of formula (II).According to another particularly preferred embodiment, theliquid-crystalline medium comprises one or more compounds of formula (I)and one or more compounds of formula (VI).

According to another preferred embodiment of the invention, X is,identically or differently on each occurrence, selected from F, Cl, CNand an alkyl or alkoxy group having 1 to 8 C atoms. It is particularlypreferred that X is selected from F, Cl, and an alkyl group having 1 to8 C atoms, and it is very particularly preferred that X is F. These arepreferred embodiments for compounds according to formulas (I), (II),(III), (IV), (V) and/or (VI).

According to a preferred embodiment, compounds according to formula (I)are selected from compounds according to formulas (I-A) and (I-B),

where R¹¹ and R¹² are defined as above,

are defined asabove; and

-   Z¹¹ and Z¹² are, identically or differently, selected from CO—O—,    —O—CO—, —CF₂O—, —OCF₂—, —OCH₂—, —CH₂O—, —CH₂CH₂— and a single bond,    with the proviso that at least one of Z¹¹ and Z¹² is not a single    bond.

For compounds according to formula (I) and formula (I-A) and (I-B), itis preferred that R¹¹ is H, F, Cl, CN, R¹—O—CO—, R¹—CO—O—, an alkyl oralkoxy group having 1 to 10 C atoms or an alkenyl or alkenyloxy grouphaving 2 to 10 C atoms, where one or more H atoms in the groupsmentioned above may be replaced by F or Cl, and where one or more CH₂groups in the groups mentioned above may be replaced by —O—CO— or—CO—O—, with R¹ being defined as above.

For compounds according to formula (I) and formula (I-A) and (I-B), itis preferred that R¹² is selected from F, Cl, alkyl and alkoxy groupshaving 1 to 3 C atoms, and alkenyl and alkenyloxy groups having 2 to 3 Catoms, with the proviso that in the above-mentioned groups two or more Hatoms are replaced by F.

For compounds according to formula (I) and formula (I-A) and (I-B),according to a more preferred embodiment, R¹² is selected from F or thefollowing groups R¹²⁻¹ to R¹²⁻³⁸

From these groups, R¹² is particularly preferred to be F or OCF₃.

For compounds according to formula (I) and formula (I-A) and (I-B), itis furthermore preferred that

are, identically or differently, selected from

where X is defined as above.

According to a more preferred embodiment of the invention, in compoundsaccording to formula (I) and formula (I-A) and (I-B),

is selected from

According to another preferred embodiment, in compounds according toformula (I) and formula (I-A) and (I-B),

is selected from

Particularly preferred embodiments of compounds according to formula(I-A) are compounds of the following formulas (I-A-1) to (I-A-4)

whereX is defined as above and is preferably, identically or differently, analkyl group having 1 to 8 C atoms, F, or Cl;R¹¹ is H, F, Cl, CN, R¹—O—CO—, R¹—CO—O—, an alkyl or alkoxy group having1 to 10 C atoms or an alkenyl or alkenyloxy group having 2 to 10 Catoms, where one or more H atoms in the groups mentioned above may bereplaced by F or Cl, and where one or more CH₂ groups in the groupsmentioned above may be replaced by —O—CO— or —CO—O—, with R¹ beingdefined as above;R¹² is selected from F, Cl, alkyl and alkoxy groups having 1 to 3 Catoms, and alkenyl and alkenyloxy groups having 2 to 3 C atoms, with theproviso that in the above-mentioned groups two or more H atoms arereplaced by F; and

are, identically or differently, selected from

Particularly preferred embodiments of compounds according to formula(I-A-1) are compounds of the following formulas (I-A-1a) to (I-A-1 g)

whereR¹¹ is defined as above, andR¹² is selected from F and the above groups R¹²⁻¹ to R¹²⁻³⁸.

Particularly preferred embodiments of compounds according to formula(I-A-2) are compounds of the following formulas (I-A-2a) to (I-A-2g)

whereR¹¹ is defined as above, andR¹² is selected from F and the above groups R¹²⁻¹ to R¹²⁻³⁸.

Particularly preferred embodiments of compounds according to formula(I-A-3) are compounds of the following formulas (I-A-3a) to (I-A-3g)

whereR¹¹ is defined as above, andR¹² is selected from F and the above groups R¹²⁻¹ to R¹²⁻³⁸.

Particularly preferred embodiments of compounds according to formula(I-A-4) are compounds of the following formulas (I-A-4a) to (I-A-4g)

whereR¹¹ is defined as above, andR¹² is selected from F and the above groups R¹²⁻¹ to R¹²⁻³⁸.

According to a preferred embodiment, in compounds of formula (I-B),exactly one of Z¹¹ and Z¹² is a single bond and the other is selectedfrom CO—O—, —O—CO—, —CF₂O—, —OCF₂—, —OCH₂—, —CH₂O— and —CH₂CH₂—.

Even more preferably, in compounds of formula (I-B), Z¹¹ is a singlebond and Z¹² is selected from CO—O—, —O—CO—, —CF₂O—, —OCF₂—, —OCH₂—,—CH₂O— and —CH₂CH₂—.

Preferred embodiments of compounds according to formula (I-B) arecompounds according to the following formulas (I-B-1) to (I-B-14)

whereR¹¹ is H, F, Cl, CN, R¹—O—CO—, R¹—CO—O—, an alkyl or alkoxy group having1 to 10 C atoms or an alkenyl or alkenyloxy group having 2 to 10 Catoms, where one or more H atoms in the groups mentioned above may bereplaced by F or Cl, and where one or more CH₂ groups in the groupsmentioned above may be replaced by —O—CO— or —CO—O—, with R¹ beingdefined as above;R¹² is selected from F, Cl, alkyl and alkoxy groups having 1 to 3 Catoms, and alkenyl and alkenyloxy groups having 2 to 3 C atoms, with theproviso that in the above-mentioned groups two or more H atoms arereplaced by F; and

are, identically or differently, selected from

is selected from

andX is defined as above and is preferably, identically or differently, For Cl.

Particularly preferably, in compounds according to formula (I-B) andformulas (I-B-1) to (I-B-14),

is selected to be

More preferably, in compounds according to formula (I-B) and formulas(I-B-1) to (I-B-14),

are selected to be

According to another preferred embodiment,

is selected to be

is selected to be

with X being defined as above.

According to a preferred embodiment, in compounds according to formula(II),

-   R²¹ is selected from H, an alkyl group having 1 to 10 C atoms and an    alkenyl group having 2 to 10 C atoms, where one or more H atoms in    the groups mentioned above may be replaced by F or Cl.

According to a further preferred embodiment, in compounds according toformula (II),

-   R²² is selected from H, F, Cl, CN or an alkyl or alkoxy group having    1 to 10 C atoms and an alkenyl or alkenyloxy group having 2 to 10 C    atoms, where one or more H atoms in the groups mentioned above may    be replaced by F or Cl.

According to a further preferred embodiment, in compounds according toformula (II),

are, identically or differently, selected from

where X is defined as above.

According to another preferred embodiment, in compounds according toformula (II),

Z²¹ is selected from —CO—O—, CH₂CH₂— and a single bond.

According to a more preferred embodiment, Z²¹ is a single bond.

Preferred embodiments of compounds according to formula (II) arecompounds of the following formulas (II-1) to (II-5)

where R²¹, R²² and X are defined as above.

Most preferred embodiments of compounds according to formula (II-1) arecompounds of the following formulas (II-1a) to (II-1c)

where

-   R²¹ is H, an alkyl group having 1 to 10 C atoms or an alkenyl group    having 2 to 10 C atoms; and-   R²² is H, an alkyl group having 1 to 10 C atoms or an alkenyl group    having 2 to 10 C atoms, where one or more H atoms may be replaced by    F or Cl.

Most preferred embodiments of compounds according to formula (II-2) arecompounds of the following formulas (II-2a) to (II-2d)

where

-   R²¹ and R²² are, identically or differently, H, an alkyl group    having 1 to 10 C atoms or an alkenyl group having 2 to 10 C atoms.

Most preferred embodiments of compounds according to formula (II-3) arecompounds of the following formulas (II-3a) and (II-3b)

where

-   R²¹ is H, an alkyl group having 1 to 10 C atoms or an alkenyl group    having 2 to 10 C atoms.

Most preferred embodiments of compounds according to formula (II-4) arecompounds of the following formulas (II-4a) and (II-4b)

where

-   R²¹ is H, an alkyl group having 1 to 10 C atoms or an alkenyl group    having 2 to 10 C atoms.

Most preferred embodiments of compounds according to formula (II-5) arecompounds of the following formulas (II-5a) and (II-5b)

where

-   R²¹ and R²² are, identically or differently, H, an alkyl group    having 1 to 10 C atoms or an alkenyl group having 2 to 10 C atoms.

In an preferred embodiment of the invention, compounds according toformula (III) are compounds according to formula (III-A) or (III-B)

where

-   R³¹ is H, CN, NCS, R¹—O—CO—, R¹—CO—O—, an alkyl, alkoxy or    thioalkoxy group having 1 to 10 C atoms, or an alkenyl, alkenyloxy    or thioalkenyloxy group having 2 to 10 C atoms, where one or more    CH₂ groups in the groups mentioned above may be replaced by O, S,    —O—CO— or —CO—O—, with R¹ being defined as above;-   R³² is H, an alkyl or alkoxy group having 1 to 10 C atoms or an    alkenyl or alkenyloxy group having 2 to 10 C atoms;-   Z³¹ and Z³² are, identically or differently, selected from CO—O—,    —O—CO—, —CF₂O—, —OCF₂—, —OCH₂—, —CH₂O—, —CH₂CH₂— and a single bond,    with the proviso that at least one of Z³¹ and Z³² is not a single    bond; and

are defined as above.

According to a preferred embodiment, in compounds according to formula(III), (III-A) and (III-B), R³¹ is CN, R¹—O—CO—, R¹—CO—O—, an alkyl oralkoxy group having 1 to 10 C atoms or an alkenyl or alkenyloxy grouphaving 2 to 10 C atoms, where one or more CH₂ groups in the groupsmentioned above may be replaced by —O—CO— or —CO—O—, with R¹ beingdefined as above.

According to one preferred embodiment, compounds according to formula(III-A) are compounds of the following formulas (III-A-1) to (III-A-3)

where

-   R³¹ is selected from H, alkyl and alkoxy groups having 1 to 10 C    atoms, and alkenyl and alkenyloxy groups having 2 to 10 C atoms; and-   R³² is selected from H, alkyl and alkoxy groups having 1 to 10 C    atoms, and alkenyl and alkenyloxy groups having 2 to 10 C atoms; and

are, identically or differently, selected from

with X being defined as above and preferably being F.

Preferably, in compounds according to formulas (III-A-1) to (III-A-3),

are, identically or differently, selected from

According to another preferred embodiment, in compounds according toformulas (III-A) and (III-B),

are, identically or differently, selected from

with X being defined as above and preferably being F.

Particularly preferred compounds according to formula (III-A) accordingto this preferred embodiment are compounds of the formulas (III-A-4) to(III-A-11)

where

-   R³¹ is selected from H, alkyl groups having 1 to 10 C atoms, or    alkenyl groups having 2 to 10 C atoms; and-   R³² is selected from H, alkyl or alkoxy groups having 1 to 10 C    atoms, or alkenyl or alkenyloxy groups having 2 to 10 C atoms.

According to a preferred embodiment, in compounds of formula (III-B),exactly one of Z³¹ and Z³² is a single bond and the other is selectedfrom CO—O—, —O—CO—, —CF₂O—, —OCF₂—, —OCH₂—, —CH₂O— and —CH₂CH₂—.

Even more preferably, in compounds of formula (III-B), Z³¹ is a singlebond and Z³² is selected from CO—O—, —O—CO—, —CF₂O—, —OCF₂—, —OCH₂—,—CH₂O— and —CH₂CH₂—.

According to a preferred embodiment of the invention, in compoundsaccording to formula (III-B),

are on each occurrence, identically or differently, selected from

where X is defined as above and is preferably F.

Preferred embodiments of compounds according to formula (III-B) arecompounds of the formulas (III-B-1) to (III-B-14)

where

-   R³¹ is selected from H, alkyl or alkoxy groups having 1 to 10 C    atoms, and alkenyl or alkenyloxy groups having 2 to 10 C atoms;-   R³² is selected from H, alkyl or alkoxy groups having 1 to 10 C    atoms, and alkenyl groups having 2 to 10 C atoms;

are on each occurrence, identically or differently, selected from

and

-   X is defined as above and is preferably F.

According to a further preferred embodiment of the invention, incompounds according to formula (VI),

is selected from

and a single bond; andX is defined as above.

According to a preferred embodiment of the invention, the totalconcentration of the compounds of the formula (I) is between 5 and 100%.More preferably, the concentration of the compounds according to formula(I) is between 10 and 98%, most preferably between 20 and 97%.

According to a more preferred embodiment of the invention, the totalconcentration of the compounds of the formula (I-A) is between 5 and100%. More preferably, the concentration of the compounds according toformula (I-A) is between 10 and 98%, most preferably between 20 and 97%.

According to a most preferred embodiment of the invention, the totalconcentration of the compounds of the formulas (I-A-2) and (I-A-3) isbetween 5 and 100%. More preferably, the concentration of the compoundsaccording to formulas (I-A-2) and (I-A-3) is between 10 and 98%, mostpreferably between 20 and 97%.

It is furthermore preferred that the total concentration of thecompounds of formula (II) is between 0 and 60%. More preferably, theconcentration of the compounds according to formula (II) is between 0and 55%.

It is furthermore preferred that the total concentration of thecompounds of the formulas (I) and (II) is between 20 and 100%. Morepreferably, the concentration of the compounds according to formulas (I)and (II) is between 30 and 100%, most preferably between 40 and 100%.

It is furthermore preferred that the total concentration of thecompounds of the formulas (I) and (VI) is between 10 and 100%, morepreferably 20 to 100% and most preferably 40 to 100%.

It is furthermore preferred that the total concentration of thecompounds of the formula (III) is between 0 and 70%. More preferably,the total concentration of the compounds of the formula (III) is between0 and 60%. Most preferably, it is between 0 and 50%.

It is furthermore preferred that the total concentration of thecompounds of the formulas (IV) and (V) is between 0 and 40%.

It is furthermore preferred that the total concentration of thecompounds of the formula (VI) is between 0 and 60%.

The invention concerns furthermore a liquid-crystalline mediumcomprising one or more compounds of the formula (I) as defined above ina total concentration of 5 to 100%, and preferably at least one furthercompound of the formulas (II) and (III) as defined above, so that thetotal concentration of the compounds of the formulas (I), (II) and (III)is between 20 and 100%.

According to a preferred embodiment of the invention, theliquid-crystalline medium comprises at least 5 different compoundsselected from the compounds of formulas (I) to (VI). According to aparticularly preferred embodiment, the liquid-crystalline mediumcomprises at least 6 different compounds selected from the compounds offormulas (I) to (VI). According to an even more preferred embodiment,the liquid-crystalline medium comprises at least 7 different compoundsselected from the compounds of formulas (I) to (VI).

Optionally the media according to the present invention may comprisefurther liquid crystal compounds in order to adjust the physicalproperties. Such compounds are known to the expert. Their concentrationin the media according to the instant invention is preferably 0% to 30%,more preferably 0.1% to 20% and most preferably 1% to 15%.

The liquid crystal media according to the present invention may containchiral dopants as further additives in usual concentrations. Preferredchiral dopants are listed in Table E below. The total concentration ofthese further constituents is in the range of 0% to 10%, preferably 0.1%to 6%, based on the total mixture. The concentrations of the individualcompounds used each are preferably in the range of 0.1% to 3%. Theconcentration of these and of similar additives is not taken intoconsideration for the values and ranges of the concentrations of theliquid crystal components and compounds of the liquid crystal media inthis application.

The liquid crystalline media according to the invention may containstabilizers as further additives in usual concentrations. Preferredstabilizers are listed in Table F below. The total concentration of thestabilizers is in the range of 0% to 10%, preferably 0.0001% to 1%,based on the total mixture.

According to a preferred embodiment of the invention, the clearing point(the temperature of the phase transition from the nematic to theisotropic state, T(N,I)) is lower than 60° C. According to aparticularly preferred embodiment, T(N,I) is lower than 50° C. Accordingto an even more preferred embodiment, T(N,I) is lower than 40° C.

The liquid crystal media according to the present invention consist ofseveral compounds, preferably of 5 to 30, more preferably of 6 to 20 andmost preferably of 6 to 16 compounds. These compounds are mixedaccording to methods known in the art. As a rule, the required amount ofthe compound used in the smaller amount is dissolved in the compoundused in the greater amount. In case the temperature is above theclearing point of the compound used in the higher concentration, it isparticularly easy to observe completion of the process of dissolution.It is, however, also possible to prepare the media by other conventionalways, e.g. using so called pre-mixtures, which can be e.g. homologous oreutectic mixtures of compounds or using so called multi-bottle-systems,the constituents of which are ready to use mixtures themselves.

The invention concerns furthermore a process for the preparation of aliquid-crystalline medium as defined above, characterized in that one ormore compounds according to formula (I) and one or more compoundsaccording to formulas (II) to (VI) are mixed with one another andoptionally with one or more further mesogenic compounds and/oradditives.

According to a preferred embodiment of the invention, the switch elementcomprises

-   -   the liquid-crystalline medium in the form of a thin layer, and    -   at least two polarisers, preferably in the form of thin layers,        one of them positioned on one side of the liquid-crystalline        medium, the other positioned on the opposite side of the        liquid-crystalline medium.

The polarisers can be linear or circular polarisers, preferably linearpolarisers.

For linear polarisers, it is preferred that the directions ofpolarisation of the two polarisers are rotated with respect to eachother by a defined angle.

Further layers and/or elements, such as one or more separate alignmentlayers, one or more glass sheets, one or more bandblock filters and/orcolor filters to block light of certain wavelengths, for exampleUV-light, may be present. Furthermore, one or more insulating layers,such as low-emissivity films, for example, may be present. Additionally,one or more adhesive layers, one ore more protective layers, one or morepassivation layers and one or more barrier layers may be present.Optionally, a metal oxide layer, where the metal oxide may comprise twoor more different metals and where the metal oxide may be doped withhalogenide ions, preferably fluoride, may be present. Preferred is ametal oxide layer comprising one or more of the following: indium tinoxide (ITO), antimony tin oxide (ATO), aluminium zinc oxide (AZO), SnO₂and SnO₂:F (fluorine doped SnO₂). Particularly preferred is a metaloxide layer comprising ITO.

In the layer of the liquid crystalline medium, spacers may be present.Typical embodiments of the above-mentioned elements as well as theirfunction is known to the person skilled in the art.

For the purposes of this application, the term “polariser” refers to adevice or substance which blocks light of one polarisation direction andtransmits light of another polarisation direction. Likewise, the term“polariser” refers to a device or substance which blocks light of onekind of circular polarisation (right-handed or left-handed) whereas ittransmits light of the other kind of circular polarisation (left-handedor right-handed).

The blocking may occur by reflection and/or absorption. A reflectivepolariser therefore reflects light of one polarisation direction or onekind of circular polarisation and transmits light of the oppositepolarisation direction or other kind of circular polarisation; and anabsorptive polariser absorbs light of one polarisation direction or onekind of circular polarisation and transmits light of the oppositepolarisation direction or other kind of circular polarisation. Thereflection or absorption is typically not quantitative, leading to thepolarisation of light by the polariser not being perfect.

According to the present invention, both absorptive and reflectivepolarisers may be used in the switch element. Preferably, the polarisersaccording to the invention represent optical thin films. Examples ofreflective polarisers which can be used according to the invention areDRPF (diffusive reflective polariser film, by 3M), DBEF (dual brightnessenhanced film, by 3M), layered-polymer distributed Bragg reflectors(DBR) as described in U.S. Pat. No. 7,038,745 and U.S. Pat. No.6,099,758 and APF (advanced polariser film, by 3M). Furthermore,wire-grid-polarisers (WGP), which reflect infrared light, as describedin U.S. Pat. No. 4,512,638, for example, may be used. Wire-gridpolarizers which reflect in the visible and ultraviolet part of thespectrum are described in U.S. Pat. No. 6,122,103, for example, and mayalso be used according to the invention. Examples of absorptivepolarisers which may be used according to the invention are Itos XP38polarising film or Nitto Denko GU-1220DUN polarising film. Examples ofcircular polarisers which can be used according to the invention areAPNCP37-035-STD (left handed) and APNCP37-035-RH (right handed) fromAmerican Polarizers Inc.

According to the invention, the switch element is thermoresponsive,signifying that its switching state is determined by temperature. In apreferred embodiment of the invention, no electrical wiring, circuitryand/or switching network is present in the switch element.

The switching of the switch element occurs between a bright or openstate of the switch element in which a higher proportion of radiantenergy is transmitted and a dark or shut state of the switch element inwhich a smaller proportion of radiant energy is transmitted.

Radiant energy is defined as above and is understood to compriseelectromagnetic radiation in the UV-A region, VIS region andnear-infrared region. Naturally, the switch element is not equallyeffective over the complete spectrum of radiant energy as defined above.Preferably, the switch element blocks a high proportion of NIR andVIS-light in the shut state, particularly preferably a high proportionof NIR light.

Also preferred are switch elements that switch in one of the ranges VISor NIR only as well as combinations switching in one range andpermanently blocking the other, for example switching VIS andpermanently blocking NIR.

According to a preferred embodiment of the invention, the switching iseffected by a change in the physical condition of the liquid-crystallinemedium. This change in the physical condition of the liquid-crystallinemedium is temperature-dependent. Preferably, it is a phase transition.According to a particularly preferred embodiment of the invention, theswitching is effected by a phase transition of the liquid-crystallinemedium from a liquid-crystalline phase to an isotropic phase which takesplace at a particular temperature. Even more preferably, the switchingis effected by a phase transition of the liquid-crystalline medium froma nematic phase to an isotropic phase.

Typically, the liquid-crystalline medium is in the isotropic state at atemperature above the phase-transition temperature and in aliquid-crystalline, preferably nematic state at a temperature below thephase-transition temperature.

Since the switching of the device is due to a temperature-dependentchange in the physical condition of the liquid-crystalline medium, theliquid-crystalline medium represents the thermoresponsive element of theoptical switch. However, further thermoresponsive elements may bepresent.

For the use of the switch to regulate the radiation energy flow betweenan interior space and the environment, preferably between a room of abuilding and the exterior, it is desirable that the switch operates at atemperature which is typical for the exterior of buildings. Preferably,the switching temperature of the switch element is between −20 and 80°C., more preferably between 10 and 60° C. and most preferably between 20and 50° C.

The switching temperature is defined to be the temperature of the switchelement. Typically, this temperature is similar to the outside airtemperature. However, under some conditions, for example under directexposure to sunlight, it may differ significantly from the outside airtemperature. Also, in the case of certain device setups, for examplewhen the switch element is located inside of an insulated glass unit,the temperature of the switch element may differ significantly from theoutside air temperature.

According to a preferred embodiment of the invention, as stated above,the switching of the switch element is effected by a change in thephysical condition of the liquid-crystalline medium. More preferably,this change in physical condition represents a phase transition whichtakes place at a certain phase transition temperature. Preferably, thephase transition temperature is between −20 and 80° C., more preferablybetween 10 and 60° C. and most preferably between 20 and 50° C.

In a highly preferred embodiment of the present invention, the plane ofpolarisation of polarised light is rotated by the liquid-crystallinemedium by a defined value if it is in the liquid-crystalline state. Incontrast, the plane of polarisation of polarised light is not rotated bythe liquid-crystalline medium if it is in the isotropic state. It is afurther aspect of this preferred embodiment, that the directions ofpolarisation of the polarisers are not identical to each other, butrotated against each other by a defined angle.

In this preferred embodiment, the two states of the device arecharacterized as follows:

In the bright or open state, incoming light is polarised linearly by thefirst polariser. The linearly polarised light then passes through theliquid-crystalline medium in its liquid-crystalline state, which leadsto its direction of polarisation being rotated by a defined angle.

After passing the liquid-crystalline medium, the linearly polarisedlight then hits the second polariser. A defined fraction of the lighthitting the polariser is transmitted through the polariser. Preferably,there is an identity or only a relatively small divergence, mostpreferably an identity of the value by which the planes of polarisationof the two polarisers are rotated against each other and the value bywhich the plane of polarisation of the polarised light is rotated by theliquid-crystalline medium in its nematic state.

Here, the value by which the plane of polarisation of the polarisedlight is rotated by the liquid-crystalline medium is understood to bethe angle formed between the plane of polarisation before entering themedium and the plane of polarisation after leaving the medium. Thisangle can in principle be between 0° and 180°. According to this, a turnby an angle X being larger than 180° is equivalent to a turn by X minusn*180°, the integer n being chosen so that the resulting angle X′ is inthe range 0°≦X′<180°.

However, it is to be noted that the liquid-crystalline medium may causea twisting of the plane of polarisation of the polarised light passingit which has an absolute value larger than 180°. Even a rotation by morethan one complete turn (360°), for example 2¼ turns or 3¾ turns mayoccur according to the invention. However, the net value by which theplane of polarisation of polarised light is rotated from entering toleaving the liquid-crystalline medium is still in any case between 0°and 180°, as has been explained above.

Obviously, depending on the reference system used, the angle by whichthe plane of polarisation is rotated may also be represented as rangingfrom −90° to 90°, negative values meaning right-turns, positive valuesmeaning left-turns.

In the bright state, due to the small divergence between the value bywhich the planes of polarisation of the two polarisers are rotatedagainst each other and the value by which the plane of polarisation ofthe polarised light is rotated by the liquid-crystalline medium, a largefraction of the light which has passed the first polariser also passesthe second polariser.

In order for the above-described bright state to occur, it is requiredthat the liquid-crystalline medium is in its liquid-crystalline state.Typically, this is the case at a temperature below the phase-transitiontemperature. Therefore, according to this preferred embodiment, theswitch element is in the bright state, when it is at a temperature whichis below the switching temperature.

In order for the dark transparent or shut state to occur, it is requiredthat the liquid-crystalline medium is in the isotropic state. In thiscase, incoming light is again linearly polarised by the first polariser.The polarised light then passes through the liquid-crystalline mediumbeing in its isotropic state. The liquid-crystalline medium in theisotropic state does not rotate the direction of polarisation oflinearly polarised light.

After passing the liquid-crystalline medium, the linearly polarisedlight with its direction of polarisation maintained hits the secondpolariser. The direction of polarisation of the second polariser is, asdescribed above, rotated with respect to the direction of polarisationof the first polariser, which is in this case, as explained above, alsothe direction of polarisation of the linearly polarised light hittingthe second polariser.

Due to the directions of polarisation of the polarized light and thepolariser not being coincident, but rotated with respect to each otherby a defined value which identical to the value by which the twopolarisers are rotated against each other, only a fraction of the lightis now transmitted. The amount of light transmitted in this state issmaller than the amount of light transmitted in the bright state.

As described above, in the dark or shut state, the liquid-crystallinemedium is in its isotropic state. Typically, this is the case at atemperature above the phase-transition temperature. Therefore, accordingto this preferred embodiment, the switch element is in the dark or shutstate, when it is at a temperature which is above the switchingtemperature.

The directions of polarisation of the two polarisers may be rotated withrespect to each other by any arbitrary value, depending on the desiredtransmission of the switch element in the dark transparent state.Preferred values are in the range of 45° to 135°, more preferred 70° to110°, most preferred 80° to 100°.

The value by which the liquid-crystalline medium in its nematic staterotates the plane of polarisation of polarised light does not have to beidentical to the value by which the directions of polarisation of thetwo polarisers are rotated with respect to each other. Preferably, thevalues are similar, with a preferred deviation of very preferably lessthan 30° and most preferably less than 20°.

The value by which the liquid-crystalline medium in its nematic staterotates the plane of polarisation of polarised light is preferably inthe range of 0° to 360°. However, values of larger than 360° may also bepresent according to the invention.

For the purpose of regulating the temperature of the interior ofbuildings, the setup described above is generally preferred. At lowtemperatures, the flow of radiant energy is allowed since the switchelement is in the open state. This leads to an increase in the heatuptake of the building, reducing heating costs. At high temperatures,the switch element is in the shut state, limiting the flow of radiantenergy into the building. This decreases unwanted heat uptake at hightemperatures, reducing the costs for air conditioning.

Depending on the angle by which the two polarisers are offset againsteach other, and also depending on whether the polarisers polarise all ofthe incoming light or only a fraction of it, more or less light istransmitted through the switch element in the shut state. With perfectpolarisers in a “crossed” position (direction of polarisation rotated by90° against each other), no light is transmitted in the shut state. Ifthe direction of polarisation of the polarisers is rotated by an angledifferent than 90°, some light is transmitted even in the shut state.Such an arrangement is desirable according to the invention.

Similarly, the amount of light which is transmitted through the switchelement in the open state depends, among other factors, on theefficiency of the polarisers and on the difference between the angle bywhich the liquid-crystalline medium rotates the direction ofpolarisation of linearly polarised light and the angle by which thedirections of polarisation of the two polarisers are rotated againsteach other. With perfect polarisers and an exact congruence of theangles of rotation, up to 50% of the light is transmitted through thedevice in the open state and, ideally, 0% of the light is transmitted inthe shut state.

The rejection of 50% of the light is due to the fact that a perfectlinear polariser rejects (by absorption or reflection) 50% of incomingunpolarised light. The transmittance of light through the device cantherefore be raised significantly if non-perfect polarisers are used,which may be desirable.

It should be mentioned here that numerous other combinations ofpolariser orientations and rotation of the direction of polarised lightdue to the liquid-crystal medium can be used within the presentinvention.

Other embodiments of the present invention comprise a liquid-crystallinemedium which scatters light when it is within a first temperature rangeand which is transparent within a second temperature range, whereas thissecond temperature range may be above or below the first temperaturerange. According to another embodiment of the present invention, theliquid-crystalline medium may affect the polarisation state ofcircularly polarised light.

According to a further embodiment of the present invention, theliquid-crystalline medium represents a guest-host system whichcomprises, in addition to one or more liquid-crystalline compounds, dyemolecules or other materials which show absorptive or reflectiveproperties. According to this embodiment, the liquid-crystalline mediumprovides orientation for the dye molecules when in theliquid-crystalline state (low temperature), but does not provide suchorientation when in the isotropic state (high temperature). Since thedye molecules interact with light in a different manner depending ontheir degree of orientation, the guest-host-system showstemperature-dependent transmission properties. According to the presentinvention, when the liquid-crystalline medium represents a guest-hostsystem, it may be preferable to use only one polarizer or no polarizerat all in the devices according to the invention. Furthermore accordingto the present invention, when the liquid-crystalline medium representsa guest-host system, a twisted nematic orientation of theliquid-crystalline medium or a vertically aligned orientation of theliquid-crystalline medium is preferably used.

According to a preferred embodiment of the invention, the rotation ofpolarised light by the liquid-crystalline medium in theliquid-crystalline state is caused by an alignment of the molecules ofthe liquid-crystalline medium. According to the invention, thisalignment is typically effected by alignment layers which are in directcontact with the liquid-crystalline medium. Preferentially, thealignment layers represent the two outer boundaries of theliquid-crystalline medium layer. For example, two alignment layersfacing each other may be attached to the interior of the compartmentenclosing the liquid-crystalline medium. According to another preferredembodiment, the alignment layers constitute the compartment enclosingthe liquid-crystalline medium. The alignment layers may be prepared byrubbing a polymer or polymer film with a rubbing cloth, a sandpaper orsome other suitable material. Polyimide films are particularly suitablefor this, but orientation may be achieved also on other kinds ofpolymers.

According to a further preferred embodiment, the alignment layer and thepolariser layer are not separate but form one single layer. They may,for example, be glued or laminated together. The property of inducing analignment of the liquid-crystalline molecules may for example beconferred to the polariser by rubbing, scratching and/or micropatterningthe polariser layer. For details, it is referred to patent applicationUS 2010/0045924, whose disclosure is hereby incorporated by reference.

A preferred embodiment of the switch element according to the inventioncomprises the liquid-crystalline medium within a container oftransparent material, preferably a transparent polymer or glass.

Furthermore, the switch element comprises two or more alignment layerswhich are in direct contact with the liquid-crystalline medium. Forexample, the alignment layers can be attached to the inner surface ofthe above-mentioned container. According to another preferredembodiment, the inner container surface can serve as an alignment layeritself.

Furthermore, the switch element comprises two or more polarisers whichmay be present in the form of polarising foils, as disclosed above.Further rigid or flexible layers may be present, such as additionalglass sheets, bandblock filters such as UV-blocking films and/orinsulating layers such as low-emissivity films. According to thisembodiment of the invention, the switch element is rigid and cannot bebent or rolled up for storage and/or transport due to the presence oflayers of rigid material.

According to another preferred embodiment of the invention, theliquid-crystalline medium is enclosed by a flexible polymer sheet. Thisflexible polymer sheet may represent the polariser and/or the alignmentlayer. Further layers, such as described above, may be additionallypresent. For details, it is referred to patent application US2010/0045924, whose disclosure is hereby incorporated by reference.According to this embodiment, the switch element is flexible and can bebent and/or rolled up.

According to another preferred embodiment of the invention, theliquid-crystalline medium has a solid or gel-like consistency. Accordingto this embodiment, a rigid container for the liquid-crystalline mediumis not required, eliminating the need for glass and/or rigid polymersheets to be present in the switch element. An advantage of thisembodiment of the invention is that the switch element is lessvulnerable to damage and can be produced in the form of thin flexiblesheets which can be rolled up. The switch element can then be cut fromthis roll in any shape or size, which simplifies storage, transport andproduction of the device.

To obtain the above-mentioned solid or gel-like consistency of theliquid-crystalline medium, the following procedures can be usedaccording to the invention.

The liquid-crystalline medium may, for example, be embedded in the formof discrete compartments such as microdroplets of liquid-crystallinemedium, within an optically transparent medium. The opticallytransparent medium preferably is a polymeric material, particularlypreferably an isotropic thermoplastic, duroplastic or elastomericpolymer. Particularly preferably, the polymeric material is athermoplastic or elastomeric polymer.

Examples for this are NCAP-films (NCAP=nematic curvilinear alignedphases) and PDLC-films (PDLC=polymer dispersed liquid crystal). NCAPfilms may be obtained by a process in which the encapsulating polymericmaterial, for example polyvinyl alcohol, the liquid-crystalline mediumand a carrier material, such as water, are mixed thoroughly in a colloidmill. Afterwards, the carrier material is removed, for example byevaporation. A detailed procedure for the formation of NCAP-films isdescribed in U.S. Pat. No. 4,435,047.

PDLC-films, which are described for example in U.S. Pat. No. 4,688,900;WO 89/06264; EP 0272585 and Mol. Cryst. Liq. Cryst. Nonlin. Optic, 157,(1988), 427-441, may be obtained by homogeneously mixing theliquid-crystalline medium with monomers and/or oligomers which willlater react to the polymer matrix. After polymerisation, a phaseseparation is induced, in which compartments or microdroplets of liquidcrystalline medium form, which are dispersed within the polymer matrix.

According to another embodiment of the invention, the liquid-crystallinemedium is present as a continuous phase within a polymer network(PN-systems). Such systems are described in detail in EP 452460, EP313053 and EP 359146, for example. The polymer network typically has aspongy structure, in which the liquid-crystalline medium can floatfreely. According to a preferred embodiment, it is formed bypolymerisation of mono- or polyacrylate monomers.

Preferably, the liquid-crystalline medium is present in PN-systems in apercentage of more than 60%, particularly preferably in a percentage of70-95%. The polymer network systems can be prepared by inducing apolymerisation reaction in a mixture comprising the liquid-crystallinemedium and the respective monomers and/or oligomers which form thethree-dimensional polymer network. According to a preferred embodiment,the polymerisation is started by photoinitiation.

According to another embodiment of the invention, the polymer does notform a network, but is dispersed in the form of small particles withinthe liquid-crystalline medium, which is present as a continuous phase asin PN-network systems.

The liquid-crystalline media according to the present invention areparticularly suitable for use in the above-mentioned PDLC-, NCAP- andPN-systems.

Further subject of the present invention is therefore a composite systemcomprising a liquid-crystalline medium as defined above and a polymer,preferably a microporous polymer.

According to the present invention, the switch element can be attachedto transparent windows, facades, doors or roofs of any kind, includingthose present in private, public and commercial buildings, in containersfor transport, storage and inhabitation and in any vehicles.Particularly preferred is the attachment to insulated glass units (IGU)or multipane windows and/or the use as an integrated element ofinsulated glass units or multipane windows. According to a preferredembodiment of the invention, the switch element is attached at theoutside-facing side of the window, facade, door or roof. According toanother preferred embodiment, the switch element is placed in theinterior of an IGU, where it is protected from adverse effects such asextreme weather conditions and from degradation due to UV exposure. Inan alternative embodiment, the switch element is attached at theinside-facing side of the window, facade, door or roof.

According to one embodiment of the invention, the switch element coversthe complete surface of the window. In this case, the control over theradiant energy flow by the switching of the device is maximised.

According to another embodiment of the invention, the switch elementcovers only parts of the surface of the window, so that there are gapsleft which are not covered by the switch element. These gaps may takethe form of stripes, spots and/or larger areas. This could allow thatsome parts of a window can be switched between a bright state and a darkstate, whereas other parts remain bright at all times. This leads to thetransparency of the window especially in the shut state to be increased.

The switch element may be used according to the invention to regulatethe radiant energy flow between an interior space and the environment.Particularly preferably, it is used for regulating the energy flow inthe form of VIS-light and NIR-light or VIS-light only or combinations ofregulated VIS-light and permanently blocked NIR-light. It is furthermorepreferred that the switch element regulates the radiant energy flowautomatically, without the need for manual controlling, by itscapability of temperature-dependent switching between an open state anda shut state. According to a particularly preferred embodiment of theinvention, the switch element is used to regulate the interiortemperature of a building and/or a vehicle.

For the purposes of the present invention, all concentrations are,unless explicitly noted otherwise, indicated in mass percent and relateto the corresponding mixture or mixture component, unless explicitlyindicated otherwise.

The clearing points of liquid-crystalline mixtures are determined incapillary tubes. A suitable instrument is Mettler Toledo FP90.Typically, liquid-crystalline mixtures show a clearing range. Accordingto our definition, the clearing point is the lowest temperature of thatrange where the whole material is still nematic.

Alternatively, clearing points of a mixture in a display can bedetermined in normally white-mode TN-cells in a microscope hot stage.The beginning of the transition from the nematic to the isotropic stateleads to black spots in the TN-cell. When heating up, the temperature atwhich such spots first occur is determined to be the clearing point.

For applications according to the present invention, long-term storagebehaviour of the liquid-crystalline media in displays is relevant. Fordetermination of the long-term storage behaviour in displays, theliquid-crystalline mixture is filled into several TN-cells with athickness of 5 to 6 μm. The TN-cells receive an end-seal, get polarisersattached for normally white mode setup and are stored for up to 1000hours in a refrigerator at a given temperature. At defined timeintervals, the TN-cells are inspected visually for dark spots indicatingcrystallisation or smectic-nematic transitions. If the TN-cells do notshow spots at the end of the testing period, the test is passed.Otherwise, the time elapsed until the first spots are detected is notedas a measure of long-term storage stability.

In the present application and especially in the following examples, thestructures of the liquid crystal compounds are represented byabbreviations, which are also called “acronyms”. Tables A to C show thestructural elements of the compounds together with their correspondingabbreviations.

All groups C_(n)H_(2n+1), C_(m)H_(2m+1), C_(p)H_(2p+1) and C_(q)H_(2q+1)are preferably straight chain alkyl groups with n, m, p and q C-atoms,respectively. All groups C_(n)H_(2n), C_(m)H_(2m), C_(p)H_(2p) andC_(k)H_(2q) are preferably (CH₂)_(n), (CH₂)_(m), (CH₂)_(p) and(CH₂)_(q), respectively; and —CH═CH— preferably is trans-respectively Evinylene. The Indices n, m, p and q preferably have a value between 1and 10.

Remark: From left side to right side in the chemical structure, theindices used are n, if only one index occurs; n and m if two indicesoccur; n, m and p if three indices occur; and n, m, p and q if fourindices occur. This nomenclature may be extended if necessary.

Therefore, a right-hand-side alkyl group —C_(n)H_(2n+1) corresponding to−n according to the acronym nomenclature (see table below) may also be agroup —C_(m)H_(2m+1) corresponding to −m, or a group —C_(p)H_(2p+1)corresponding to −p, or a group —C_(q)H_(2q+1) corresponding to −q,depending on the index which is chosen. The same applies for all othergroups of Table C where a letter n is used signifying an alkyl grouphaving n carbon atoms and 2n+1 hydrogen atoms or an alkylene grouphaving n carbon atoms and 2n hydrogen atoms.

Table A lists the symbols used for the ring elements, table B those forthe linking groups and table C those for the symbols for the left handand the right hand end groups of the molecules.

TABLE A Ring Elements C

P

D

DI

A

AI

G

GI

U

UI

Y

M

MI

N

NI

Np

n3f

n3fI

Th

thI

th2f

th2fI

o2f

o2fI

Dh

K

KI

L

LI

F

FI

TABLE B Linking Groups E —CH₂—CH₂— V —CH═CH— T —C≡C— W —CF₂—CF₂— B—CF═CF— Z —CO—O— ZI —O—CO— X —CF═CH— XI —CH═CF— O —CH₂—O— OI —O—CH₂— Q—CF₂—O— QI —O—CF₂—

TABLE C End Groups Left hand side, used alone or in Right hand side,used alone or in combination with others combination with others -n-C_(n)H_(2n+1)— -n —C_(n)H_(2n+1) -nO- C_(n)H_(2n+1)—O— -On—O—C_(n)H_(2n+1) -V- CH₂═CH— -V —CH═CH₂ -nV- C_(n)H_(2n+1)—CH═CH— -nV—C_(n)H_(2n)—CH═CH₂ -Vn- CH₂═CH—C_(n)H_(2n)— -Vn —CH═CH—C_(n)H_(2n+1)-nVm- C_(n)H_(2n+1)—CH═CH—C_(m)H_(2m)— -nVm—C_(n)H_(2n)—CH═CH—C_(m)H_(2m+1) -N- N≡C— -N —C≡N -S- S═C═N— -S —N═C═S-F- F— -F —F -CL- Cl— -CL —Cl -M- CFH₂— -M —CFH₂ -D- CF₂H— -D —CF₂H -T-CF₃— -T —CF₃ -MO- CFH₂O— -OM —OCFH₂ -DO- CF₂HO— -OD —OCF₂H -TO- CF₃O—-OT —OCF₃ -A- H—C≡C— -A —C≡C—H -nA- C_(n)H_(2n+1)—C≡C— -An—C≡C—C_(n)H_(2n+1) -NA- N≡C—C≡C— -AN —C≡C—C≡N Left hand side, used incombination Right hand side, used in with others only combination withothers only - . . . n . . . - —C_(n)H_(2n)— - . . . n . . .—C_(n)H_(2n)— - . . . M . . . - —CFH— - . . . M . . . —CFH— - . . . D .. . - —CF₂— - . . . D . . . —CF₂— - . . . V . . . - —CH═CH— - . . . V .. . —CH═CH— - . . . Z . . . - —CO—O— - . . . Z . . . —CO—O— - . . . ZI .. . - —O—CO— - . . . ZI . . . —O—CO— - . . . K . . . - —CO— - . . . K .. . —CO— - . . . W . . . - —CF═CF— - . . . W . . . —CF═CF—wherein n and m each are integers and three points “ . . . ” indicatethat other symbols of this table may be present at the position.

The structures in the following tables D1 and D2 are preferred compoundsfor use in the device according to the invention.

The structures which are listed in table D1 are given together withtheir acronym names according to the system represented above.

TABLE D1 Illustrative Structures

TABLE D2 Further Illustrative Structures

Table E lists chiral dopants, which are preferably used in the liquidcrystalline media according to the present invention.

TABLE E

In a preferred embodiment of the present invention the media accordingto the present invention comprise one or more compounds selected fromthe group of compounds of table E.

Table F lists stabilizers, which are preferably used in the liquidcrystalline media according to the present invention.

TABLE F

Remark: In this table “n” means an integer in the range from 1 to 12.

In a preferred embodiment of the present invention, the media accordingto the present invention comprise one or more compounds selected fromthe group of compounds of table F.

EXAMPLES

The following exemplary liquid-crystalline mixtures are listed for thepurpose of illustrating the present invention and are not to beunderstood as limiting it in any way.

The compositions of the liquid-crystalline mixtures are listed belowtogether with their clearing points and their long-term-storagebehaviour. The person skilled in the art learns from the data givenbelow which properties can be obtained with the mixtures according tothe invention. He is furthermore taught how the composition of themixtures can be modified in order to obtain the desired properties, inparticular a defined temperature of the clearing point and highlong-term stability.

Liquid crystal mixtures with the compositions listed in the followingtables are prepared, and their clearing points and long-term-storagebehaviour are determined.

As stated in the description part of the present application, theclearing point of the liquid-crystalline media according to theinvention is preferably between −20 and 80° C., more preferably between10 and 60° C. and most preferably between 20 and 50° C. Even morepreferably, the clearing point is between 20 and 40° C.

Exemplary mixtures with a relatively high clearing point (>70° C., inparticular >80° C.) are preferably used as a so-called two-bottle systemin combination with a mixture having a lower clearing point.

1) Examples for Liquid-Crystalline Media According to the Invention

Example-1 Example-2 Clearing 66° C. 36° C. point Storage >1000 h >1000 hstability at −40° C. Substance % Substance % CGU-2-F 8 CGU-2-F 8 CGU-3-F10 CGU-3-F 10 CGU-5-F 8 CGU-5-F 8 CPU-3-F 14 CPU-2-F 8 CPU-5-F 11CPU-3-F 14 PGU-2-F 7 CPU-5-F 11 PGU-3-F 9 PGU-2-F 7 PGU-5-F 9 PGU-3-F 9CPG-3-F 8 PGU-5-F 9 CPG-5-F 6 CCU-2-F 6 CPP-3-2 4 CP-5-3 10 CPPC-3-3 4CPPC-5-3 3 sum 100 100 Example-3 Example-4 Clearing 35° C. 32.5° C.point Storage >1000 h >1000 h stability at −40° C. Substance % Substance% CPG-3-F 4 CPG-3-F 4 CPU-3-F 12 CPU-3-F 12 CPU-5-F 10 CPU-5-F 10CCU-2-F 11 CCU-2-F 11 CCU-3-F 11 CCU-3-F 11 CP-7-F 9 CP-7-F 4.5 CP-5-335 CP-3-2 4.5 CPP-3-2 4 CP-5-3 35 CPPC-3-3 2 CPP-3-2 4 CPPC-5-3 2CPPC-3-3 2 CPPC-5-3 2 sum 100 100 Example-5 Clearing 7.5° C. pointStorage >1000 h stability at −40° C. Substance % CPG-3-F 4 CPU-3-F 12CPU-5-F 10 CCU-2-F 11 CCU-3-F 11 CP-7-F 4.5 CP-3-2 12.5 CP-5-3 35 sum100 Example-6 Example-7 Clearing 66° C. 40° C. point Storage >1000h >1000 h stability at −40° C. Substance % Substance % CCU-2-F 8 CCU-2-F6 CCU-3-F 11 CCU-3-F 9 CGU-2-F 8 CGU-2-F 8 CGU-3-F 11 CGU-3-F 11 CGU-5-F10 CGU-5-F 10 CDU-2-F 9 CDU-2-F 9 CDU-3-F 9 CDU-3-F 9 CDU-5-F 4 CPU-2-F3 CCEG-5-F 9 CPU-3-F 9 CCP-3-OT 8 CPU-5-F 6 CCG-3-OT 10 CP-5-3 12CPP-3-2 3 CCP-3-OT 8 sum 100 100 Example-8 Example-9 Clearing 67° C. 36°C. point Storage >1000 h >1000 h stability at −40° C. Substance %Substance % CCU-3-F 5 CCU-2-F 4 CGU-2-F 11 CCU-3-F 6 CGU-3-F 11 CCU-5-F6 CGU-5-F 7 CGU-2-F 7 CPU-3-F 13 CGU-3-F 7 CPU-5-F 10 CGU-5-F 7 CPG-2-F3 CPU-3-F 13 CCZU-2-F 5 CPU-5-F 10 CCZU-3-F 15 CP-5-3 21 CCZU-5-F 4CCZU-2-F 5 CCP-3-OT 3 CCZU-3-F 10 CCZG-2-OT 10 CCZU-5-F 4 CPP-3-2 3 sum100 100 Example-10 Example-11 Clearing 69° C. 36° C. point Storage >1000h >1000 h stability at −40° C. Substance % Substance % CGU-2-F 9 CGU-2-F9 CGU-3-F 4 CGU-3-F 4 CCU-2-F 8 CCU-2-F 8 CC-5-V 18 CPU-2-F 4 CC-3-V1 9CPU-3-F 8 CC-3-T 8 CC-5-V 18 CCZU-2-F 5 CC-3-V1 9 CCZU-3-F 15 CC-3-T 8CCP-3-OT 6 CP-7-F 6 CGZP-2-OT 10 CP-5-3 11 CGZP-3-OT 8 CCZU-2-F 5CCZU-3-F 10 sum 100 100 Example-12 Example-13 Clearing 35° C. 69° C.point Storage >1000 h >1000 h stability at −40° C. Substance % Substance% CGU-2-F 4 CCU-2-F 8 CGU-3-F 4 CCY-3-F 11 CGU-5-F 4 CCP-3-OT 8 CP-7-F 8CCG-3-OT 10 CP-3-2 20 CGU-2-F 8 CCY-3-2 10 CGU-3-F 11 CGP-3-2 6 CGU-5-F10 CGP-5-2 4 CDU-2-F 9 PUP-2-5 7 CDU-3-F 9 PGU-3-3 7 CDU-5-F 4 CYP-2-1 7CCEG-5-F 9 CPU-2-0 7 CPP-3-2 3 CPU-3-O2 5 CPP-0-3 7 sum 100 100Example-14 Clearing 32° C. point Storage 1000 h stability at −40° C.Substance % CCP-3-OT 5 CCP-4-OT 5 CCP-5-OT 4 CPPC-3-3 4 CPPC-5-3 4CPPC-5-5 4 CGPC-3-3 4 CGPC-5-3 4 CGPC-5-5 4 CCZPC-3-3 4 CCZPC-3-4 4CCZPC-3-5 3 Y-4O-O5 8 Y-2O-O4 8 Y-3O-O5 7 Y-3O-O3 7 Y-6O-O6 7 Y-5O-O6 7Y-4O-O6 7 sum 100

2) Use of Liquid-Crystalline Media in Switch Elements

The mixtures 1 to 14 according to the invention are employed asliquid-crystalline media in the switch element according to theprocedure of US 2009/0015902.

For assembling the switch element, the procedure described in paragraphs[0050]-[0055] of the above-mentioned patent application is followed,except that instead of the mixture disclosed in the application (5 parts6CB (4′-hexyl-4-cyanobiphenyl), 1.25 parts mixture E7 and 0.008 partsS-811) one of the exemplary mixtures of the present invention is used(example-1 to example-11).

With the mixtures according to the invention (Example-1 to Example-14),switch elements with high operational lifetime can be obtained. Theswitch elements have a switching temperature which is close to theclearing point of the mixtures (10° C. to 80° C., which is in thepreferred operating range of the elements).

This shows that high device stability together with a controllableclearing point can be obtained with the mixtures according to theinvention.

These findings support the concept of the present invention forliquid-crystalline mixtures for use in switch elements.

The invention claimed is:
 1. A switch element that is thermoresponsiveand is capable of switching between a less transmissive state forradiant energy and a more transmissive state for radiant energy, saidswitch element comprising: a liquid-crystalline medium, which comprisesone or more compounds of formula (I)

where R¹¹ is H, F, Cl, CN, NCS, R¹—O—CO—, R¹—CO—O—, an alkyl, alkoxy orthioalkoxy group having 1 to 10 C atoms, or an alkenyl, alkenyloxy orthioalkenyloxy group having 2 to 10 C atoms, where one or more H atomsin the groups mentioned above are each optionally replaced by F, Cl, orCN, and where one or more CH₂ groups in the groups mentioned above areeach optionally replaced by O, S, —O—CO— or —CO—O—; R¹² is selected fromF, Cl, alkyl and alkoxy groups having 1 to 10 C atoms, and alkenyl andalkenyloxy groups having 2 to 10 C atoms, with the proviso that in theabove-mentioned groups one or more H atoms are replaced by F or Cl; R¹is, identically or differently on each occurrence, an alkyl or analkenyl group having 1 to 10 C atoms, in which one or more H atoms areeach optionally replaced by F or Cl;

are selected from

is selected from

X is on each occurrence, identically or differently, F, Cl, Br, CN or analkyl, alkoxy or thioalkoxy group having 1 to 10 C atoms, where one ormore H atoms in the groups mentioned above are each optionally replacedby F or Cl and where one or more CH₂ groups are each optionally replacedby O or S; Y is on each occurrence, identically or differently, selectedfrom H and X; and Z¹¹ and Z¹² are, identically or differently, selectedfrom CO—O—, —O—CO—, —CF₂O—, —OCF₂—, —OCH₂—, —CH₂O—, —CH₂CH₂— and asingle bond, wherein said liquid crystalline medium has a phasetransition temperature between 20° C. and 50° C., and wherein saidswitch element is suitable for the regulation of radiant energy flowbetween an interior space and the environment.
 2. A switch elementaccording to claim 1, wherein said liquid-crystalline medium furthermorecomprises one or more compounds of formula (III)

where R³¹ is H, CN, NCS, R¹—O—CO—, R¹—CO—O—, an alkyl, alkoxy orthioalkoxy group having 1 to 10 C atoms, or an alkenyl, alkenyloxy orthioalkenyloxy group having 2 to 10 C atoms, where one or more CH₂groups in the groups mentioned above are each optionally replaced by O,S, —O—CO— or —CO—O—; R³² is H, an alkyl or alkoxy group having 1 to 10 Catoms, or an alkenyl or alkenyloxy group having 2 to 10 C atoms; and

are on each occurrence, identically or differently, selected from

Y and X are defined as in claim 1; and Z³¹ and Z³² are, identically ordifferently, selected from CO—O—, —O—CO—, —CF₂O—, —OCF₂—, —OCH₂—,—CH₂O—, —CH₂CH₂— and a single bond.
 3. A switch element according toclaim 1, wherein said liquid-crystalline medium furthermore comprisesone or more compounds of formulas (IV), (V) and (VI)

where R⁴¹, R⁴², R⁵¹, R⁵², R⁶¹, R⁶² are on each occurrence, identicallyor differently, selected from H, F, Cl, CN, NCS, R¹—O—CO—, R¹—CO—O—, analkyl, alkoxy or thioalkoxy group having 1 to 10 C atoms and an alkenyl,alkenyloxy or thioalkenyloxy group having 2 to 10 C atoms, where one ormore H atoms in the groups mentioned above are each optionally replacedby F or Cl, and where one or more CH₂ groups in the groups mentionedabove are each optionally replaced by O, S, —O—CO— or —CO—O—; R¹ isdefined as in claim 1;

are, identically or differently, selected from

is selected from

and a single bond; Y is on each occurrence, identically or differently,selected from H and X; X is defined as in claim 1; and Z⁴¹ to Z⁴³ andZ⁵¹ to Z⁵⁵ are, identically or differently, selected from —CO—O—,—O—CO—, —CF₂O—, —OCF₂—, —CH₂CH₂—, —OCH₂—, —CH₂O— and a single bond.
 4. Aswitch element according to claim 2, wherein compounds according toformula (I) are selected from compounds according to formulas (I-A) and(I-B),

where R¹¹ and R¹² are defined as in claim 3,

are defined as in claim 2; and Z¹¹ and Z¹² are, identically ordifferently, selected from CO—O—, —O—CO—, —CF₂O—, —OCF₂—, —OCH₂—,—CH₂O—, —CH₂CH₂— and a single bond, with the proviso that at least oneof Z¹¹ and Z¹² is not a single bond.
 5. A switch element according toclaim 4, wherein R¹² is selected from F or the following groups R¹²⁻¹ toR¹²⁻³⁸


6. A switch element according to claim 4, wherein compounds according toformula (I-A) are compounds of the following formulas (I-A-1) to (I-A-4)

where X is as defined; R¹¹ is H, F, Cl, CN, R¹—O—CO—, R¹—CO—O—, an alkylor alkoxy group having 1 to 10 C atoms or an alkenyl or alkenyloxy grouphaving 2 to 10 C atoms, where one or more H atoms in the groupsmentioned above are each optionally replaced by F or Cl, and where oneor more CH₂ groups in the groups mentioned above are each optionallyreplaced by —O—CO— or —CO—O—; R¹ is as defined; R¹² is selected from F,Cl, alkyl and alkoxy groups having 1 to 3 C atoms, and alkenyl andalkenyloxy groups having 2 to 3 C atoms, with the proviso that in theabove-mentioned groups two or more H atoms are replaced by F; and

are, identically or differently, selected from


7. A switch element according to claim 4, wherein compounds according toformula (I-B) are compounds according to the following formulas (I-B-1)to (I-B-14)

where R¹¹ is H, F, Cl, CN, R¹—O—CO—, R¹—CO—O—, an alkyl or alkoxy grouphaving 1 to 10 C atoms or an alkenyl or alkenyloxy group having 2 to 10C atoms, where one or more H atoms in the groups mentioned above may bereplaced by F or Cl, and where one or more CH₂ groups in the groupsmentioned above may be replaced by —O—CO— or —CO—O—; R¹ is as defined;R¹² is selected from F, Cl, alkyl and alkoxy groups having 1 to 3 Catoms, and alkenyl and alkenyloxy groups having 2 to 3 C atoms, with theproviso that in the above-mentioned groups two or more H atoms arereplaced by F;

are, identically or differently, selected from

is selected from

and X is as defined.
 8. A switch element according to claim 1, wherein Xis selected from F, Cl, and an alkyl group having 1 to 8 C atoms.
 9. Aswitch element according to claim 1, wherein the total concentration ofthe compounds of the formula (I) is between 5 and 100%.
 10. A switchelement according to claim 1, wherein no electrical wiring, circuitryand/or switching network is present in the switch element.
 11. Aliquid-crystalline medium comprising: one or more compounds of theformula (I) in a total concentration of 5 to 100%:

where R¹¹ is H, F, Cl, CN, NCS, R¹—O—CO—, R¹—CO—O—, an alkyl, alkoxy orthioalkoxy group having 1 to 10 C atoms, or an alkenyl, alkenyloxy orthioalkenyloxy group having 2 to 10 C atoms, where one or more H atomsin the groups mentioned above are each optionally replaced by F, Cl, orCN, and where one or more CH₂ groups in the groups mentioned above areeach optionally replaced by O, S, —O—CO— or —CO—O—; R¹² is selected fromF, Cl, alkyl and alkoxy groups having 1 to 10 C atoms, and alkenyl andalkenyloxy groups having 2 to 10 C atoms, with the proviso that in theabove-mentioned groups one or more H atoms are replaced by F or Cl; R¹is, identically or differently on each occurrence, an alkyl or analkenyl group having 1 to 10 C atoms, in which one or more H atoms areeach optionally replaced by F or Cl;

are selected from

is selected from

X is on each occurrence, identically or differently, F, Cl, Br, CN or analkyl, alkoxy or thioalkoxy group having 1 to 10 C atoms, where one ormore H atoms in the groups mentioned above are each optionally replacedby F or Cl and where one or more CH₂ groups are each optionally replacedby O or S; Y is on each occurrence, identically or differently, selectedfrom H and X; and Z¹¹ and Z¹² are, identically or differently, selectedfrom CO—O—, —O—CO—, —CF₂O—, —OCF₂—, —OCH₂—, —CH₂O—, —CH₂CH₂— and asingle bond; and one or more compounds of formula II-2a

wherein R²¹ and R²² are, identically or differently, H, an alkyl grouphaving 1 to 10 C atoms or an alkenyl group having 2 to 10 C atoms;and/or one or more compounds of formula VI

wherein R⁶¹ and R⁶² are on each occurrence, identically or differently,selected from H, F, Cl, CN, NCS, R¹—O—CO—, R¹—CO—O—, an alkyl, alkoxy orthioalkoxy group having 1 to 10 C atoms and an alkenyl, alkenyloxy orthioalkenyloxy group having 2 to 10 C atoms, where one or more H atomsin the groups mentioned above may be replaced by F or Cl, and where oneor more CH₂ groups in the groups mentioned above may be replaced by O,S, —O—CO— or —CO—O—, R¹ is as defined in formula (I),

is selected from

and a single bond; Y is on each occurrence, identically or differently,selected from H and X; X is as defined in formula (I); and wherein saidliquid crystalline medium has a phase transition temperature between 20°C. and 50° C.
 12. A thermoresponsive optical switch element comprising aliquid-crystal medium according to claim
 11. 13. A composite systemcomprising a liquid-crystalline medium according to claim 11 and apolymer.
 14. A method for the regulation of the flow of radiant energybetween an interior space and the environment, comprising regulatingsaid flow with a switch element according to claim
 1. 15. A compositesystem according to claim 13, wherein said polymer is a microporouspolymer.
 16. A liquid-crystalline medium according to claim 11, whereinsaid medium contains said one or more compounds of formula II-2a in atotal concentration of at least 10%.